Question

Why don't alkanes have geometric isomers?

Answer 1

Because, generally, their structure affords them no opportunity for geometric isomerism.

Explanation:

An alkane could have two chiral centres (and this give a pair of diastereomers), however, this is a fairlyy contrived circumstance.

An alkane has general formula `C_nH_(2n+2)`. When we draw them out we depict the most symmetric structure possible, a straight chain. With no chiral centres, and no olefinic bonds, geometric isomerism cannot be supported.